Azure Functions Event Hubs - Java

This project demonstrates an Azure Functions application written in Java that processes messages from Azure Event Hubs. It includes an Event Hub trigger function that reads messages from an input Event Hub, processes them, and sends the processed messages to an output Event Hub.

Features

• Event Hub Trigger: Automatically processes messages from an input Event Hub
• Event Hub Output Binding: Sends processed messages to an output Event Hub
• Java: Azure Functions v4 programming model with Java annotations
• Infrastructure as Code: Complete Bicep templates for Azure resources
• Azure Developer CLI: Streamlined deployment with azd

Architecture

Input Event Hub → Azure Function → Output Event Hub
                      ↓
              Application Insights

Prerequisites

• Java 21 or later
• Apache Maven 3.8+
• Azure Functions Core Tools v4
• Azure Developer CLI (azd)
• Azure CLI
• An Azure subscription

Project Structure

.
├── src/
│   └── main/
│       └── java/
│           └── com/
│               └── function/
│                   ├── EventHubsTrigger.java   # Event Hub trigger function
│                   └── TimerTrigger.java        # Timer trigger to generate test messages
├── infra/                                       # Bicep infrastructure files
│   ├── main.bicep                               # Main deployment template
│   ├── app/
│   │   ├── api.bicep                            # Function App configuration
│   │   ├── eventhubs.bicep                      # Event Hub resources
│   │   ├── rbac.bicep                           # Role assignments
│   │   └── vnet.bicep                           # Virtual network
│   ├── abbreviations.json                       # Resource naming conventions
│   └── main.parameters.json                     # Deployment parameters
├── pom.xml                                      # Maven build configuration
├── host.json
└── azure.yaml                                   # Azure Developer CLI configuration

Function Logic

The EventHubsTrigger function:

1. Receives messages from the input Event Hub
2. Parses and processes each message
3. Adds metadata (ID, timestamp)
4. Sends processed messages to the output Event Hub
5. Logs processing information to Application Insights

Local Development

1. Build the Project

mvn clean package

2. Configure Local Settings

Create or update local.settings.json:

{
  "IsEncrypted": false,
  "Values": {
    "AzureWebJobsStorage": "UseDevelopmentStorage=true",
    "FUNCTIONS_WORKER_RUNTIME": "java",
    "EventHubConnection__fullyQualifiedNamespace": "<your-eventhub-namespace>.servicebus.windows.net",
    "INPUT_EVENTHUB_NAME": "input-events",
    "OUTPUT_EVENTHUB_NAME": "output-events"
  }
}

3. Run Locally

mvn clean package
mvn azure-functions:run

Deploy to Azure

Using Azure Developer CLI (Recommended)

1. Login to Azure:

   azd auth login

2. Initialize the environment:

   azd env new

   Enter an environment name (e.g., "dev").

3. Build and deploy:

   mvn clean package
   azd up

This command will:

• Create all Azure resources (Event Hubs, Function App, Storage, Application Insights)
• Deploy your function code
• Configure all connections and settings

Manual Deployment

1. Create Azure resources:

   az group create --name rg-eventhubs-java --location eastus
   az deployment group create --resource-group rg-eventhubs-java --template-file infra/main.bicep

2. Deploy function code:

   mvn clean package
   func azure functionapp publish <function-app-name>

Testing

Send Test Messages

Use Azure CLI to send test messages to the input Event Hub:

az eventhubs eventhub message send \
  --namespace-name <your-namespace> \
  --eventhub-name input-events \
  --messages '[{"id": "1", "message": "Hello from CLI"}]'

Monitor Function Execution

1. View logs in the portal:

   • Navigate to your Function App in Azure Portal
   • Go to "Monitor" → "Logs"

2. View in Application Insights:

   az monitor app-insights query \
     --app <app-insights-name> \
     --analytics-query "traces | where message contains 'Event hub function' | order by timestamp desc | take 20"

3. Check output Event Hub:

   • Verify processed messages in the output Event Hub using Azure Portal or Event Hub Explorer

Configuration

Environment Variables

Variable	Description
EventHubConnection__fullyQualifiedNamespace	Event Hub namespace (uses managed identity)
INPUT_EVENTHUB_NAME	Name of the input Event Hub
OUTPUT_EVENTHUB_NAME	Name of the output Event Hub
APPLICATIONINSIGHTS_CONNECTION_STRING	Application Insights connection string

Managed Identity

The Function App uses managed identity to connect to Event Hubs. The infrastructure automatically assigns the "Event Hubs Data Owner" role to both your user account and the Function App's managed identity.

Troubleshooting

Function not triggering

• Verify the Event Hub connection string and names
• Check that messages are being sent to the input Event Hub
• Review Application Insights logs for errors

Authentication errors

• Ensure managed identity is enabled on the Function App
• Verify role assignments (Event Hubs Data Owner) are configured
• Check that the namespace FQDN is correct in settings

Node.js errors

• Run npm install to ensure all dependencies are installed
• Verify Node.js version (22.x or later)

Clean Up

To delete all Azure resources:

azd down

Or manually:

az group delete --name rg-eventhubs-javascript

Resources

• Azure Functions JavaScript Developer Guide
• Azure Event Hubs Documentation
• Azure Developer CLI
• Bicep Documentation

License

This project is licensed under the MIT License.